Gelled fluids have been used for pipeline cleaning, well stimulation, and for cleaning well bores, but the most common and economically important use for gelled fluids in hydrocarbon recovery is in formation fracturing, which is well known. See, for example, Smith et al U.S. Pat. No. 5,417,287, McCabe et at U.S. Pat. No. 5,514,645, Graham et al U.S. Pat. Nos. 6,004,908 and 6,147,034, and Taylor et at U.S. Pat. Nos. 6,511,944, 6,544,934, and 7,341,103. The gelled liquid is sent down the well under great pressure and through perforations in the well casing, where it causes fractures in the earth formation. The gelled fluid is used to suspend and transport a hard granular material such as sand, known as a “proppant” for its function of maintaining the openings of the fissures so the recovered oil or gas can be drawn from the formation into the recovery system.
Phosphate esters are widely used in the hydrocarbon recovery industry to form the basis of the gel, after crosslinking by injecting sources of iron or aluminum, as is known in the art.
Partially because of the stresses on the gel from being forced through the well casing perforations and from flowing under pressure in contact with the irregular surfaces in the formation fractures, it has been difficult for workers in the art to assure adequate stability of the gel when it finally reaches the smaller fissures and interstices in the formation comprising the ultimate destination of the proppant. Whether it is in an aqueous or a hydrocarbon base, the gel is vulnerable to degradation from the stress of such surface contact and turbulence-inducing pathways under great pressure; the turbulent proppant itself also exerts physical stress on the molecular structure of the gel. There is a need in the art for more stable gels, and particularly for stable crosslinkers that form the gels, yet the gels must also be readily pumpable and susceptible to breaking when it is necessary to assure the flow of hydrocarbons from the fractured formation. In addition to these basic performance criteria, there is an increasing need for hydrocarbon gels having a demonstrable ability to carry sand and other proppants at very cold temperatures.